In order to overcome the difficulty of key management in “one time pad” encryption schemes and also resist the attack of chosen plaintext, a new image encryption algorithm based on chaos and SHA-256 is proposed in this paper. The architecture of confusion and diffusion is adopted. Firstly, the surrounding of a plaintext image is surrounded by a sequence generated from the SHA-256 hash value of the plaintext to ensure that each encrypted result is different. Secondly, the image is scrambled according to the random sequence obtained by adding the disturbance term associated with the plaintext to the chaotic sequence. Third, the cyphertext (plaintext) feedback mechanism of the dynamic index in the diffusion stage is adopted, that is, the location index of the cyphertext (plaintext) used for feedback is dynamic. The above measures can ensure that the algorithm can resist chosen plaintext attacks and can overcome the difficulty of key management in “one time pad” encryption scheme. Also, experimental results such as key space analysis, key sensitivity analysis, differential analysis, histograms, information entropy, and correlation coefficients show that the image encryption algorithm is safe and reliable, and has high application potential.

In this paper, we construct a five dimensional continuous hyperchaotic system and propose an image encryption scheme based on the hyperchaotic system, which adopts DNA dynamic coding mechanism and classical scrambling diffusion encryption structure. In the diffusion stage, two rounds of diffusion are adopted and the rules of DNA encoding (DNA decoding) are dynamically changed according to the pixel value of the plaintext image, that is, the rules of DNA encoding (DNA decoding) used to encrypt different images are different, which makes the algorithm can resist chosen-plaintext attack. The encryption (decryption) key is only the initial value of the chaotic system, which overcomes the difficulty of key management in the “one time pad” encryption system. The experimental results and security analysis show that the algorithm has some advantages of large key space, no obvious statistical characteristics of ciphertext, sensitivity to plaintext and key and able to resist differential attacks and chosen plaintext attack. It has good application prospects.

In this paper, a five-dimensional discrete hyperchaotic map is constructed by combining Logistic map and 3D discrete Lorenz map. Based on this chaotic system, a block-based image encryption scheme related to plaintext is designed. The encryption scheme includes scrambling operation and diffusion operation. In the scrambling operation, the scrambling sequence is related to the pixels of the plaintext image, while in the diffusion operation, two rounds of diffusion are carried out for intra-block diffusion, and the generation of random diffusion sequence is related to a pixel value in the block in each round of diffusion, which makes the algorithm resist chosen-plaintext attack. When the next block is diffused, the generation of the diffusion sequence is related to the first and last pixels of the previous block, which makes the block and block interact with each other and enhances the sensitivity of the algorithm to plaintext. Theoretical analysis and experimental results demonstrate the security and practicability of the cryptosystem.

In this paper, a novel image compression–encryption hybrid algorithm is proposed. Firstly, a Gauss random matrix and a random scrambling matrix are generated by using Chebyshev mapping and Logistic mapping respectively. Then, based on the principle that a scrambling Gauss matrix is still a Gauss matrix, a compression scheme for ciphertext images is designed. It is dependent on the Gauss random matrix and the random scrambling matrix, which mainly consists of three parts: permutation-based encryption using random scrambling matrix by Alice, encoding with Gauss random matrix by Charlie, and joint decryption and decoding by Bob. It has a special application scenario, that is, Alice requires semi integrity Charlie to transmit images to Bob through a channel. Experimental results show that the scheme has strong robustness against noise and chosen-plaintext attack,and further the peak signal to noise ratio (PSNR) and subjective visual quality of reconstructed images can be improved by comparing with the similar methods.

This paper analyzes the security of image encryption systems based on bit plane extraction and multi chaos. It includes a bit-level permutation for high, 4-bit planes and bit-wise XOR diffusion, and finds that the key streams in the permutation and diffusion phases are independent of the plaintext image. Therefore, the equivalent diffusion key and the equivalent permutation key can be recovered by the chosen-plaintext attack method, in which only two special plaintext images and their corresponding cipher images are used. The effectiveness and feasibility of the proposed attack algorithm is verified by a MATLAB 2015b simulation. In the experiment, all the key streams in the original algorithm are cracked through two special plaintext images and their corresponding ciphertext images. In addition, an improved algorithm is proposed. In the improved algorithm, the generation of a random sequence is related to ciphertext, which makes the encryption algorithm have the encryption effect of a “one time pad”. The encryption effect of the improved algorithm is better than that of the original encryption algorithm in the aspects of information entropy, ciphertext correlation analysis and ciphertext sensitivity analysis.

At present, the probability density of most chaotic systems is unknown, and the statistical characteristics of chaotic sequences can not be described by the probability density of chaotic maps. This paper constructes a class of quadratic polynomial chaotic maps with three system parameters which are topologically conjugated with Tent maps. The probability density functions of this kind of chaotic maps are given. Then, an arcsine function is designed to transform the chaotic sequence generated by the quadratic polynomial chaotic map into a new random sequence, which obeys the uniform distribution on the interval (-0.5, 0.5). In order to show the application of the new uniform random numbers, the applications of it in generating random arrangement, Gaussian measurement matrix of compressed sensing and pseudo random number generator are discussed.